Re: CPUs and processes not evenly assigned?!

[Hubert Feyrer <hubert%feyrer.de@localhost>]

On Thu, 10 Nov 2016, Michael van Elst wrote:
> > > Can you try this?
>
> > Tried it, and it seems to help with both 2 and 4 CPUs.
> > Codebase: -current
>
> Great, so the problem was just the rounding error.

Yes. I've also played with it a bit more, and the "stealing" of processes 
between CPUs seems to get less with the factor of r_mcount, e.g. with 4* 
below I see less movement of processes on a 4-CPU system as shown in the 
patch below.

Maybe this should be made a sysctl or depend on the number of CPUs?


 - Hubert



--- sys/kern/kern_runq.c.orig   2016-11-10 21:11:10.000000000 +0000
+++ sys/kern/kern_runq.c
@@ -534,7 +534,9 @@ sched_balance(void *nocallout)
                ci_rq = ci->ci_schedstate.spc_sched_info;

                /* Average count of the threads */
-               ci_rq->r_avgcount = (ci_rq->r_avgcount + ci_rq->r_mcount) >> 1;
+               ci_rq->r_avgcount = (ci_rq->r_avgcount +
+                       4*ci_rq->r_mcount
+                       ) /2;

                /* Look for CPU with the highest average */
                if (ci_rq->r_avgcount > highest) {


 - Hubert